A contextualized reinforcer pathology approach to addiction

Abstract

Behavioural economic accounts of addiction conceptualize harmful drug use as an operant reinforcer pathology, emphasizing that a drug is consumed because of overvaluation of smaller immediate rewards relative to larger delayed rewards (delay discounting) and high drug reinforcing value (drug demand). These motivational processes are within-individual determinants of behaviour. A third element of learning theory posits that harmful drug use depends on the relative constraints on access to other available activities and commodities in the choice context (alternative reinforcers), reflecting the substantial influence of environmental factors. In this Perspective, we integrate alternative reinforcers into the contemporary behavioural economic account of harmful drug use - the contextualized reinforcer pathology model - and review empirical literature across the translational spectrum in support of this model. Furthermore, we consider how increases in drug-related mortality and health disparities in addiction can be understood and potentially ameliorated via a contextualized reinforcer pathology model in which lack of alternative reinforcement is a major risk factor for addiction.

Keywords: Addiction; Decision making; Human behaviour; Psychology.

Fig. 1. Behavioural economic demand and delayed reward discounting.

a, Representation of a behavioural economic demand curve, which can be plotted using data from purchase tasks. As cost increases, consumption decreases. Demand indices that can be extracted from the data include intensity (consumption at zero cost), breakpoint (the price at which consumption is fully suppressed) and elasticity (the rate of change in consumption as a function of cost). b, Representation of the change in value of two rewards as a function of the delay to reward receipt. The reward from substance use is smaller, but the receipt is nearer in time, whereas the reward from an alternative is larger, but receipt is further delayed in time. When receipt of both rewards are distant in time, the value of the larger reward is greater. However, owing to the hyperbolic nature of delayed reward discounting, the value of the immediate reward increases at a greater rate as reward receipt becomes closer in time. Thus, an individual might experience a preference reversal, in which the value of the immediate reward surpasses the value of the delayed reward when receipt of the immediate reward is imminent.

Fig. 2. Situating behavioural economic theories of addiction.

a, Although most theories of addiction recognize diverse influences, disciplinary foci tend to be oriented toward person-level factors or environmental factors. b, Behavioural economics bridges the connection between environmental and within-individual determinants by framing behaviour within a discrete choice context that is heavily influenced by environmental factors; these discrete choice contexts are building blocks for patterns of behaviour over time, which aggregate into measurable individual difference variables.

Fig. 3. A contextualized reinforcer pathology approach.

Two theoretical examples depicting the effects of environmental constraints on the value of alternatives and alcohol at three time points. Blue represents reinforcement from alternative activities and red represents reinforcement from alcohol-related activities. The left panel shows a scenario most likely to result in increasing levels of substance use. Initially, substance value is low, and the individual engages in many alternative activities. However, over time the environmental context places increasingly high constraints on alternatives (the local park shuts down, the individual cannot afford to go to college, the roads are bad for biking) and low constraints on alcohol (easily available from local store, cheap, social reinforcement from drinking). Consequently, alcohol value increases over time while engagement and availability of alternatives decrease. The right panel shows a scenario that would result in stable or decreasing levels of alcohol use over time. Initially, substance value is low, and the individual engages in many alternative activities. Over time, constraints on alternatives remain low. As the individual enters emerging adulthood, they connect with friends through drinking, and therefore the value of alcohol rises slightly. However, the individual maximizes more global utility and continues to engage in available alternatives that effectively compete with the immediate rewarding effects of alcohol. Consequently, when the individual leaves college and drinking among friends declines, the individual’s drinking declines as well.

Fig. 4. Interactions between substance cost and alternative reward.

The likelihood of using a substance is based on the cost of the substance, the delay to the receipt of the alternative reward, and the value of the alternative reward. Across both plots, substance use is most likely when the substance cost is low and when the delay to the alternative is high. As the cost of the substance increases, the likelihood of use decreases. Further, as the alternative reward receipt becomes closer in time, the likelihood of use decreases. However, when there is a high-value alternative available (an activity that generates a positive affective state or sense of accomplishment or alleviates an aversive state; bottom panel) the likelihood of use across all delays and substance costs are attenuated relative to when a low-value alternative (a non-stimulating or aversive activity; top panel) is available.